Digital gain adjusters where the gain is set in decibels (dB) are usually built using a digital multiplier and a lookup table to calculate the correct coefficient to apply.
FIG. 1 illustrates a gain adjuster 100 of this type. The gain adjuster 100 comprises a linear digital multiplier 104 and a lookup table 102. The digital multiplier 104 has an input arranged to receive an n-bit digital signal, and output arranged to output the digital signal multiplied by the gain. The digital multiplier 104 also has a control input coupled to an output of the lookup table 102, for receiving a g-bit gain coefficient. The lookup table 102 receives a c-bit gain-control value representing a gain in decibels (dB). That is, each binary step of the c-bit gain control value (from one binary value to the next) represents a logarithmic step in dB. The lookup table 102 then comprises 2c elements for mapping the c-bit value to a g-bit coefficient representing a gain on a linear scale, for supply to the control input of the linear multiplier 104.